By the way, my comments about adjusting the color, saturation, and contrast do not require post processing. When I mentioned your settings in camera, and you mentioned that you use the highest JPG setting, I think you midunderstood. Your camera somewhere has a color profile in the menu - often it's called something like 'picture style' - it will usually give you some preset choices like : normal, vivid, portrait, natural, landscape, etc. Each one of these settings has adjustments available within it - say you choose 'normal'...you can then go into this mode and adjust saturation from -3 to +3, contrast from -3 to +3, sharpness from -3 to +3, etc. You need to go through the initial tuning of the camera to choose the amounts of each of these modes that suit your personal taste.

This was also shot on a badly overcast day, also in JPEG mode, and also directly from camera with no post-processing:

However, I used -.3 EV to underexpose in poor, overly bright light, and I've got my camera's contrast, color, and saturation tuned to deliver the look and feel I prefer, with a little 'pop' so it comes out a little sharper, nice colors, and deeper blacks. It doesn't have to be done in post processing, it's just a matter of learning how to set up your camera and how to adjust exposure in different conditions when the camera is wrong.

I often find the technically correct images to be really bland. I suggested to do it in post because theres a technique called "Exposing to the right" (EttR) in which you deliberately overexpose an image to get a more rich tonal range and reduce noise in shadow areas.

I think the best start on the photos would have been if the horse was back some coming into the photo but more impotantly hiding the trampoline.
The trampoline kills the photo for me because it is in focus or I can tell what it is.
It doesn't belong in a pic of a horse.
Second killer is the poor light,some days just aren't meant for taking certain types of pics,this pic and that light don't seem to work well together.

There is a menu for the picture style, but I don't totally understand it, so I don't touch it. I don't change the exposure level (needle) either as I have not tried to before, but guess I shall.

I took a variety of photographs at different apertures, but Photobucket took a while to a while to upload them, so I just put the first three up, which were all taken at the same settings, unfortunately.

"Sometimes cropping a picture can improve it dramatically.
Cropping can be used to:
* Enlarge the main subject
* Eliminate things that distract attention from the subject"

If you look at your pic #1 and imagine....

Spin the horse around where it stands in the pic or back maybe in front of the shed some.
Wait for it to lift it's head up maybe....
Without the trampoline and the swingset back there I think that line of trees alone would have a great effect on the overall pic.
The empty grass/pasture would have also.
The house/shed doesn't matter much as it is obscured from view by the bush.

The lens was a Minolta 300mm F4 APO. It was shot handheld while on vacation in Aruba. It was a very overcast, rainy day, so I used some bushes as the background to avoid the ugly white sky, and used a larger aperture to get nice blur of the background - especially useful since this was shot by the pool at a hotel, and I didn't want too much of the background to be distracting.

My camera works best for JPEGs when I set it to 'Vivid' mode - which is how mine is set up - I then adjusted the saturation to -1, contrast to 0, and sharpness to 0.

With your camera, try out some of those other modes you mentioned. Try landscape or normal. Usually, once you select one of these settings, you'll then see some other settings that can be adjusted inside each mode - like color, saturation, contrast, etc. With most cameras, you can either use the 'user settings' mode and choose all the settings yourself, or you can choose one of the preset modes and adjust the individual settings to suit your taste...the camera should remember and hold any settings changes you make in any of the picture style modes.

I prefer my custom settings a bit more aggressive, as this eliminates post processing the photo at a later time.
Also, different cameras process the photo differently so you have to find your “personal” preferences.

I jack my “vivid” all the way to +3 Saturation, and my Standard is –3 Saturation with +3 contrast/sharpness and D-R+.